I had the same goal. I ended up ordering this controller board and built a power cable for it that plugs into an USB socket.
The good news is, it works. The 5V are plenty enough when plugged directly to a 2A USB power supply. The bad news is that it doesn’t work so well when plugged to the Raspberry (+controlblock, which would’ve allowed me to power everything up and down using the controlblock’s power switch). The backlight flickers. I’ve read somewhere that reducing the brightness might help but I don’t want to do that, so right now I’m using 2 separate USB cables, one for the raspberry and one for the lcd, both plugged the same dual-output USB charger.